Condensed Matter Seminar Series
Topological Phase Transitions in Ultra-Cold Fermi Superfluids:
The Evolution from BCS to BEC under Zeeman and Spin-Orbit Fields
Carlos A. R. Sa de Melo
Friday October 14, 1:30 pm, Room 298, Physics Building
NOTE IRREGULAR DAY AND TIME!
quantum phase transitions in superfluids with non-s-wave order parameters have
been conjectured theoretically in the context of p-wave  and d-wave 
systems for many years, but never observed experimentally due to the absence of
tunable parameters. In this talk, I discuss topological phase transitions in ultra-cold
Fermi superfluids induced by interactions, artificial spin orbit, and Zeeman fields,
which are tunable parameters in the context of ultra-cold atom physics. I
construct the phase diagram of ultracold Fermi superfluids at zero and finite
temperatures, and analyze spectroscopic and thermodynamic properties to
characterize various phase transitions. For systems with zero Zeeman field, the
evolution from BCS to BEC superfluids in the presence of spin-orbit effects is
only a crossover as the system remains fully gapped , even though a triplet
component of the order parameter emerges. However, for finite Zeeman fields,
spin orbit fields induce a triplet component in the order parameter that
produces nodes in the quasiparticle excitation spectrum leading to bulk
topological phase transitions of the Lifshitz type . Additionally a fully
gapped phase exists, where a crossover from indirect to direct gap occurs, but
a topological transition to a gapped phase possessing Majorana fermions edge
states does not occur.
 G. E.
Volovik, Exotic Properties of Superfluid 3He, World Scientific, Singapore
 R. D. Duncan and C. A. R. Sa de Melo, Phys. Rev. B
62, 9675 (2000).
 Li Han, C. A. R. Sa de Melo,
 Kangjun Seo, Li Han and C. A. R. Sa de Melo,
Host: Harold Baranger